I bought a nice used low mileage '06 Screw and found that it didn't have a trac-lok installed. I'm want to get this swapped out before winter sets in and I thought it may be a good idea to swap to 3.08 gears at this time. I can't find anything on anyone going this direction. It came with 3.55 gears and 265/60/18 tires from the factory. I don't haul, tow, race or do anything that would need to be considered a quick launch. I just like the fact that the truck sets higher than cars. I'm looking to get a little better gas mileage. I've read as much as my eyes could take for tonight and I find that a lot of people say stay stock or recommend going to 4.10s. I've installed a canned tune from SCT but that is all that has been done so far. Give me your thoughts. Thanks

 

I've got 3.55 gears, I still find myself locking OD out a lot! You live in Ky, you have hills, some engine braking is a good thing. I might go through the trouble for a locker of some sort that's "switchable", but I don't believe you'll see any benefit in gas mileage with 3.08s in Ky. You'll see an increase in brake pad and rotor wear though, SCREWs are not light trucks even empty!

Going from 3.55s to 3.08s will reduce torque multiplication and engine braking to 86.7% of what it is now, and will lower RPMs by that factor.

 

I really like this product, a user shiftable tough locker:

http://www.ox-usa.com/ox/Products/Lo...9/Default.aspx

 

Keep your 3.55's - you may actually LOSE gas mileage with 3.08's.

 

Keep 3.55s. 3.08 will have no power, you won't like it. Your city mileage will definitely be lower with 3.08s and you will most likely have to downshift to go up hills on the highway with 3.08s

 

That unit appears to be designed for the 8.8 rear-end.

I live in western Ky. where it's flat.

 

This should be what you need:

http://www.drivetrainspecialists.com...duct-5441.html

 

Thanks for the link but that's not the main issue. Gear choice to finish the project is the main objective.

 

Do NOT get those 3.08s I understand your wish to net a few more MPGs, but it is not going to happen. You are going to spend longer on the throttle getting up to speed. The torque multiplication that occurs with shorter gears is really what is assisting your mileage to some degree. I drove a 2000 F-150 with a 4.6L v8 and 3.08 rear end for 5 years. It was a dog. Sure cruising down the freeway at 70 mph turning 1750 RPM seemed great, but as soon as you are in town mileage tanks. The gas mileage in my 2007 5.4 w/ 3.73 is within 1 to 1.5mpg on the highway of what the 3.08 was getting me, and around town MPG is significantly better. That's an awful lot of work and money to get maybe an extra 40-50 miles on a tank of gas (depending on tank size). If it saves you 3 gallons at the pump and you fill up once a week at an average of $3.50 per gallon, that's $10.50 a tank and it would take every bit of a year if not longer to recoup the money you dropped in re-gearing your truck.

Buy a little beater Toyota and leave your truck alone LOL.

 

Like I said, KEEP the 3.55's. There is a DARN good reason they were not a factory option for your truck. If it got better gas mileage, you BET Ford would have put them in.

That's what I posted the link for - a Truetrak is a lot better than a clutch-type LSD.

 

OK. Here's what I came up with. Keep the 3.55s add the limited slip and go to 305/45/22 tires and wheels. I should end up with a 3.31 ratio and when I get ready to sell I can just return everything to stock. Thoughts?

 

you simply refuse to pay attention


I'm gonna be gentle: don't even waste your time, money or effort as you will be disappointed

 

If I go to the effort to put the L/S in should I change the gear ratio (3.73 or 4.10) since it will be apart anyway?

 

If you are going to put those oversize tires on it, YES, put 4.10's in. You will also need a programmer to correct your speedometer/odometer.

No matter WHAT you do, you are going to lose gas mileage if you put those oversize wheels and tires on, and there is no way to get it all back.

 

Looks like I'll stick with the L/S, my 3.55s and call it a day. Thanks for all the input.